New open source projects have been launched by KDE developers aimed at bringing a consistent user interface across a varied of touch screen interfaces like tablets and entertainment devices and take data integration to a new level. The new Plasma Active and Contour projects were developed to offer a new user experience for tablets, smartphones and set top boxes.

The simple explanation is perhaps because of all the crappy websites, or simply the basic nature of the linked web. In any case the up button is a great usability feature, and it's rather puzzling other browsers do not copy it.

It's the feature i miss the most when using other browsers. Obviously I can get to the front-page of any site by selecting and deleting everything but the base URL in the address-bar, but two quick taps on the up button is both much easier and faster.